Traveling probes | Treasures of inventiveness to prolong the mission

Their mission was to last five years. But almost half a century after their launch, the two probes Voyager are always at work. A handful of NASA engineers deploy their great know-how to keep them operational.

The two probes launched in 1977 still have 10 to 15 years of hydrazine, fuel for engines. On the other hand, plutonium, the decomposition of which produces heat which feeds electricity devices, is exhausted quickly.

“If we arrive at the point where there is no longer enough plutonium, it will be a victory,” says Kareem Badaruddin, technical manager of the Voyager at NASA mission. “It will mean that we have resolved all the other problems of spaceship much older than the expected duration of their mission. »»

More recent Pepin: Voyager 1 experienced communication problems from December 2023 to April 2024.

“We have summoned a dozen NASA experts on the antennas, software, memory and electronic hardware (hardware), says Mr. Badaruddin. Finally, we understood by elimination that it was a problem of corruption of a memory unit of the central computer. It was necessary to modify all the software that used it. The Eureka moment occurred when a repetitive message, “333b”, was observed buried in incomprehensible communications.

Usually, NASA engineers do not subscribe to a popular maxim among computer scientists, “testing is doubt”, a strategy which consists in solving problems after putting a new software online. “At NASA, we are champions of doubt, we are still testing software changes to avoid unpleasant surprises in space. But with the Voyagerwe cannot test. We must trust our analyzes. It is difficult for most of us. »»

In some cases, changes can be tested on Voyager 2which is shorter than its twin.

Heat

The degradation of plutonium means that the probes lose 4.5 watts per year. “Until now, we have been able to remove the supply to the not necessary instruments, such as the high -speed transmission antenna, which requires much larger terrestrial reception antennas than what we have, and the cameras which, in any case, are useless because there is not enough light,” says Badaruddin.

A overvoltage protection system has also been abandoned.

Linda Spilker, scientific manager for traveling, sees that certain scientific instruments should soon be alternated. “We also want to minimize the heating of the hydrazine supply lines. The problem is that in some of these lines, thermometers have great uncertainty. So we may use more heating than necessary. We try to reduce this uncertainty by extrapolating from thermometers elsewhere on the probes. »»

Inversion d’octet

Another miracle occurred in the spring: the resurrection of an engine of Voyager 1 left for dead in 2004. It will not be used immediately, but will extend the life of the probe. Hydrazine tanks have silicone balloons to keep the pressure in weightlessness. However, NASA realized ten years ago that silicone dissolved in hydrazine. “It contaminates the fuel and it leaves deposits that enlighten the engines,” said Mr. Badaruddin. Some are more than 90 % blocked. »»

The engine that has not been used since 2004 had a heating problem. “The temperature was made to zero when it was to be 170 ºC,” said the engineer. It created risks of explosion because hydrazine accumulated before lighting up. »»

Suspecting a computer bug, the team looked at the problem last winter and concluded that it could be an “byte inversion” in the heating software. To confirm if that was the case, Voyager 1 was oriented with more precision than usual, to be able to close the current engine for 45 minutes. “We had a 15 -minute window to check that the heating was coming back. Now we have a spare engine. The probes have 16 engines each for orientation on three axes.

The mystery of 2020

One of the mysteries of recent years is an increase in the magnetic field and the density of plasma around Voyager 1. “We thought at the start that it was linked to a solar rash, but it has been going on for five years. We hope to be able to better understand what is going on in the coming years. »»

This zone could be linked to an irregular form of heliopause, the limit that the interstellar particles (interstellar wind) do not cross, coming from other stars. Astronomers thought that heliopause was a very precise limit, but the measures of the two Voyager seem to show that the area where the solar and interstellar winds meet is much more extensive than expected. And, therefore, that Voyager 1 has not yet reached the “pure interstellar wind” area, which it could affect, according to certain estimates, in five years.

Work up to 84

The first scientific manager of the program, Ed Stone, retired until 2022, at 84, after 50 years to take care of the two probes. And he died two years later. “He passed the torch when his wife fell ill,” said M^me Spilker, who worked 30 years on the Cassini mission. At that moment, I thought I myself retire. I am 70 years old. »»

She thinks to stay until the deaths of the two Voyager ? “Certainly until 2027, for 50 years. Then we will see. I have a very competent right arm, Jamie Rankin. And I have ten wonderful grandchildren that I would like to see more. »»

The discoveries of probes

The two probes were simply to explore Jupiter and Saturn, which they reached between 1979 and 1981. But Voyager 2 was also able to explore Uranus in 1986 and Neptune in 1989. This is the only time that the planets most distant from the sun were explored by a probe. They crossed the heliopause, the limit where the particles of the sun go, in 2012 for Voyager 1 And in 2018 for his twin. Until 2012, it was unknown where the heliopause was. In addition to the first photos of the four giant planets, and a famous photo of the earth with a distance of 6 billion kilometers in 1990 by Voyager 1 was named Pale blue pointthe probes revealed that:

• The Jovian Moon Io has volcanoes.
• Uranus and Neptune also have rings.
• Jupiter has a strong lightning activity.
• The Jovienne Europe and Saturnian Moons Enlaze have oceans under a layer of ice.
• The Neptunian Moon Triton has methane geysers.